Polystyrene, living polymer

The first living polymer studied in detail was polystyrene polymerized with sodium naphthalenide in tetrahydrofuran at low temperatures ... 

This relation was verified experimentally7 49 and it was shown that the degree of polymerization in a system containing "living polymers is independent of concentrations of initiator or monomer and of temperature. Furthermore, if all the growing centers were formed in a time much shorter than the time of polymerization, a Poisson molecular weight distribution would be obtained. Indeed, by using this technique samples of polystyrene were obtained for which MjMn = 1.04. 

Ion coupling of anionic and cationic living polymers is an interesting procedure for the synthesis of a well-defined block copolymer. Attempted coupling of the polystyrene anion with the poly-THF cation initiated by triethyloxonium tetrafluoro-borate yielded a block copolymer mixed with homopolymers394. The block ef-... 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

Anionic polymerisation of hydrocarbon monomers is initiated by lithium butyl to produce a living polymer the association number of which in solution is required to elucidate the kinetics. When the living polymer (for example polystyryl lithium) is terminated, the polystyrene can be isolated and a solution then made to determine its molecular weight, M. If the living polymer is associated in solution, the ratio of its... 

The polydispersity of polymers prepared in this way is usually very low for example, a value MJM of 1.05 was found for a sample of poly(a-methylsty-rene). Living polymers can also be used for the preparation of block copolymers after the consumption of the first monomer, a second anionically polymerizable monomer is added which then grows onto both ends of the initially formed block. By termination of the living polymer with electrophilic compounds the polymer chains can be provided with specific end groups for example, living polystyrene reacts with carbon dioxide to give polystyrene with carboxylic end groups. 

Preparation of the Living" Polystyrene. 18 g of the living polymer was prepared by standard anionic polymerization using n-butyl lithium. The reaction was carried out by the dropwise addition of 20 ml of styrene to 5 ml of the initiator solution in 150 ml of neat THF at -78°C. The styrene drip was adjusted to take approximately 30 min for completion and then the reaction was allowed to stir for two hours before the grafting reaction with mesylated lignin was carried out. The number average molecular weight of the polystyrene, as determined by HPSEC, was 9500 with polydispersity of 1.2. 

When a tetra-chain, star-shaped polystyrene is prepared by a coupling reaction between living polymer and coupler (e.g 1,2,4,5-tetrachloromethyl benzene), the reaction is often carried out with the polystyryl anion in slight excess in order to avoid by-production of types of branched polystyrene other than the tetra-chain. 

Various problems may be encountered in thermodynamic investigations of living polymers. An instructive example is provided by the studies of the styrene-living polystyrene system as reported recently by... 

I hope the reader will not be too disappointed that he had to accompany me through some fields of small-molecule or at the most middle-sized molecule chemistry and has not up to here read a word about macromole-cular chemistry, in which according to a quite general opinion, well known to me, I am said to be a special expert. As a matter of fact, except for my former activity in the field of polybutadiene and polystyrene chemistry which touched the problems later on referred to as living polymers, I was never closely connected with macromolecular chemistry. But my own life contained some surprises, and I believe the most astonishing event was my sudden confrontation with macromolecules in consequence of an experiment which led from monomeric ethylene to its lowest possible polymer, ... 

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